A Review on: Performance Evaluation of Crop Simulation Model (APSIM) in Prediction Crop Growth, Development and Yield in Semi Arid Tropics

Crop Simulation Models (CSM) are computerized representations of crop growth, development and yield, simulated through mathematical equations as functions of soil conditions, weather and management practices. The Crop simulation models like agricultural production system simulator can save time and resources better prediction accuracy is the most important point that should be considered in decision making process. Most models are not tested or poorly tested, and hence their usefulness in decision making process is unproven. Therefore, this paper Reviews the performance of the APSIM CSM simulation accuracy with respect to the simulation of the growth, development and yield of the selected crops. APSIM model is reliable crop simulation model in predicting development, Growth and yield of different crops in the semi arid tropics. Keywords: APSIM, CSM, Yield, Semi arid tropic

Apple (Malus × domestica Borkh.) bud dormancy dynamics and genetics of tree architecture under tropical and temperate climatic conditions

Apple (Malus × domestica Borkh.) is the most important of the deciduous tree fruits in terms of production and a focus of research worldwide. Today, it is cultivated widely in temperate latitudes where winter temperatures can fall below 0°C and in high elevations in the tropics and sub-tropics such as Ethiopia. Like other deciduous fruit trees, apple trees require a certain amount of winter chilling to enter into and exit from endodormancy. Hence, temperature is surely one of the principal defining characteristics of a location s suitability for apple production. In a temperate climate, the temperature of the cold autumn and winters is sufficient low to satisfy the chilling requirement of apples, but growers would like to delay budbreak and flowering (by cultivars with high chilling requirements) to avoid damage from spring frosts. In the warmer cultivation regions of the world like Ethiopia, on the other hand, this chilling requirement is not necessarily met, resulting in delayed and irregular defoliation, uneven budburst, irregular flowering and low budburst percentages. These irregularities cause management problems later in the growing season and culminate in poor adaptation, reduced yields and quality, and altered tree architecture and future productivity of the tree. To solve these problems a better knowledge of dormancy and tree growth is needed and therefore, the aim of this thesis was twofold: to describe bud dormancy dynamics and to get insight into the genetics underlying the control of tree architecture in apple in temperate and tropical climates.Bud dormancy (both para- and endo-dormancy) dynamics was investigated for two cultivars, Golden Delicious and Gala grafted on M9 rootstock, in areas with contrasting climatic conditions (a temperate climate Belgium and a tropical highland Ethiopia) for two successive years (2010/11 and 2011/12). Moreover, a validation experiment was conducted on MM106 apple rootstock during 2010/11 only in Ethiopia. To evaluate dormancy, the inverse of time to 50% budburst was determined of the terminal bud, and of both distally and proximally situated lateral buds. Experiments were done on intact shoots, on shoots without the distal shoot piece and on shoots with a distal disbudded shoot piece. Shoots and buds on shoots can have inhibitory effects on the proximal situated buds. Results show that differences in the rates of budburst were not exclusively related to the chilling requirements of the cultivars, as cultivar × environment interactions were evident. In the temperate winter climate (Belgium), terminal buds are more endodormant than laterals, a basitonic budburst gradient achieved between the lateral buds during autumn and winter; whereas this relation was reversed during spring, in which terminal buds burst earlier than lateral buds: acrotonic gradient. In mild-winter climate (Ethiopia), on the other hand, basitonic budburst tendency remained throughout the observation period, including spring. Moreover, a stronger paradormancy inhibition by the distal shoot parts and/or buds was observed in Ethiopia than in Belgium.For the study of the genetics of tree architecture, 166 genotypes of a mapped Telamon (columnar habit) and Braeburn (normal habit) population ( T×B ) on MM106 rootstock, replicated 2-3 times per genotype both in Belgium and Ethiopia were used to examine variability of main shoot growth traits. The results were also used to identify quantitative trait loci (QTL) for tree architecture. Each of the traits analyzed exhibits continuous phenotypic variation as typical for quantitative traits. Genotype, environment and genotype-environment interaction variances were significant for most architectural traits in the first year growth, suggesting that there was considerable variability present in the genotypes and environments analyzed. Particulary it was interesting to note that the vegetative growth characteristics of genotypes showed higher variances in Ethiopia and trees were very vigorous with less branching, implicating that the warm growing season with high incidence of solar radiation and probably the clay-rich soil in Ethiopia favors apical dominance. As expected, a number of QTL were also identified on the genetic linkage maps of Telamon and Braeburn using data from individual environments and joint data analysis. In particular, a total of 40 and 54 QTL were detected in Ethiopia and Belgium on 10 and 11 genetic linkage groups respectively. These results confirm that regulation of tree architecture is complex and further suggesting that tree architectural traits in both parents are largely, but certainly not completely governed by the alleles of the Co gene per se and are real quantitative traits. Specifically, linkage group (LG) 8 of both parents, which did not entail a significant QTL for any trait in Belgium, seemed an important LG in Ethiopia for genetic expression of base diameter, tree volume and internode number. On the other hand, LGs 2, 5 and 15, were important LGs in Belgium for expression of sylleptic branching characteristics which was not the case in Ethiopia. As phenotypes and the underlying genetic expression of quantitative traits vary greatly with development, further genetic investigation on the T×B genotypes during their second year growth was carried out in Belgium; though this was not possible in Ethiopia as most of the genotypes remained dormant during the second year growth. Similarly, the genotypic effects were highly significant (p ≤ 0.001) for all traits in the second year growth in Belgium. On the other hand, fewer QTL were detected in the second year growth compared to the QTL identified in the first year. Particularly, QTL identified for the same traits were mostly different in both years and for many of the traits there was good evidence that linkage group 10 of both parents contributed to the identified QTL. Many age-specific QTL were detected as trees matured. Thus, measuring mature trees might then be the best method of detecting QTL that provide a more precise estimation of genotypic values as their phenotypic effects would accumulate over years. In conclusion, the presented results indicate that period of endodormancy is longer under conditions of low chilling and that there are also differences in paradormancy and evolution of paradormancy compared to conditions of normal chilling. This means that cultivar choice, pruning and other manipulations of trees under low chilling conditions have to be adapted compared to temperate conditions. Finally, as there is still a knowledge gap on bud dormancy under mild climates further in-depth research is imperative. Concerning the genetics of tree architecture, LG 10 seems crucial for tree architectural traits regardless of the presence or absence of the dominant Co-allele of the gene as several QTL were identified in the Braeburn parental genetic map. Moreover, results indicate that growth characteristics are under strong environmental and/or ontogenetic influence and that QTL by environment/ontogeny interactions are evident. Thus, additional research needs to be done to validate the QTL detected in the present study before any attempt to execute marker-assissted selection program.status: publishe